This invention in the general field of centrifugal blowers, particularly plastic injection-molded blowers such as those used to cool electronics in automotive applications.
Automotive electronics are often placed in areas of high ambient temperature, such as vehicle engine compartments. In order to assure that electronics remain within their design temperature limits, small centrifugal blowers are sometimes used to provide cooling. Because space is limited, these blowers must be extremely compact. In the interest of compactness, these blowers sometimes utilize an annular stator instead of a volute. A problem with this configuration, however, is that it is often inefficient when used in small, low power blowers. Another problem is that it is difficult to take advantage of the improved packaging efficiency of this configuration when using extremely inexpensive, low-power, mechanically-commutated (brushed) motors, which have a length significantly greater than their diameter. Electronically-commutated (brushless) motors are shorter, and can allow the overall blower dimensions to be reduced, but typically are significantly more expensive.
Centrifugal blowers usually employ volutes to collect the flow leaving the impeller blades and direct flow into a duct that carries the flow downstream. The direction of the flow exiting the blower is turned (e.g. generally on the order of 90xc2x0) from the direction of the flow upstream of the blower. In some cases, however, centrifugal blowers employ an annular stator that directs the flow from the impeller blades by turning the flow from a generally radial and tangential direction to a generally axial and tangential direction, thereby producing flow downstream of the blower that is generally in the same direction as that upstream of the blower. Typically the annular stator includes stator blades which reduce the tangential component of velocity. This design is best suited for reasonably large, high-power blowers, which operate at high Reynolds number, as explained below.
The blade chord Reynolds number (xe2x80x9cReynolds numberxe2x80x9d or simply xe2x80x9cRexe2x80x9d) is a non-dimensional parameter that is a measure of the relative effects of inertial forces and viscous forces in a fluid. Reynolds number is defined by the following equation:
Re=xcfx81UL/xcexc
where xcfx81 is the fluid density, U is a characteristic velocity, L is a characteristic length, and xcexc is the fluid viscosity. A small Reynolds number indicates that viscous forces dominate the behavior of a fluid, whereas a large Reynolds number indicates that inertial forces dominate the behavior of a fluid. The shapes of the impeller and stator blades are likely to differ depending on the magnitude of the Reynolds number associated with the flow conditions of the design application.
One design characteristic of centrifugal impellers is the blade curvaturexe2x80x94i.e. either forward-curved or backward-curved. Centrifugal blowers utilizing annular stators often use backward-curved impellers. Backward-curved impellers have a high degree of reactionxe2x80x94that is, there is a significant pressure rise within the impeller blading. In order to develop this pressure, the flow must remain largely attached to the blades. This can be achieved when the Reynolds number is high, but is more difficult at low Reynolds numbersxe2x80x94that is, when the impeller is small, or when the rotation speed is low. Forward-curved blades have a low degree of reaction, and do not require large Reynolds numbers to work effectively.
Centrifugal blowers with annular stators often have a two-stage stator design, where one cascade of stator blades is located behind another. An advantage of this design is that one can increase the solidity of the second stator stage, due to the fact that the flow has been turned significantly by the first stator stage. This type of stator tends to work well at large Reynolds numbers. At low Reynolds numbers, however, the amount of flow turning that can be achieved is much less, so there is less to be gained by a two-stage stator. In fact, the stator blades in the two-stage design are likely to have short chords to reduce overall package size, thus reducing the Reynolds number even further. This is another possible source of inefficiency for small, low-power, centrifugal blowers incorporating annular stators
Yapp, U.S. Pat. No. 4,900,228 discloses a centrifugal blower with backward-curved blades having an xe2x80x9cSxe2x80x9d shaped camber. The blower employs an annular two-stage stator.
Yapp, U.S. Pat. No. 4,946,348 discloses a centrifugal blower with backward-curved blades. The blower employs an annular two-stage stator.
Yapp, U.S. Pat. No. 5,743,710 discloses a centrifugal blower that employs an annular two-stage stator.
This invention features a very compact blower assembly architecture that performs well at small blower diameters and with low-powered motorsxe2x80x94conditions which tend to result in low Reynolds numbers. The blower assembly includes an impeller with forward-curved blades and a hub that is shaped to minimize the overall package volume of the assembly by covering at least 30% of the axial extent of the motor. The blower assembly also comprises a shroud comprising: i) a generally cylindrical inlet which directs the air into the impeller, and ii) a surface which directs the air leaving the impeller into a stator, turning it from a generally radial and tangential direction to a generally axial and tangential direction. The stator includes an annular region with a single stage of stator blades that reduce the tangential component of the velocity of the air entering the stator and produce a static pressure rise. The stator blade diameter is less than 150 millimeters and the stator chord lengths are at least 15% of the stator blade diameter. Input motor power is less than 25 watts.
In preferred embodiments, the blower assembly is characterized by:
a) a brushed (mechanically-commutated) direct-current motor with an input power of less than 10 watts, and, most preferably, less than 5 watts;
b) a stator blade diameter less than 90 millimeters;
c) stator blade chord lengths greater than 20% of the stator blade diameter;
d) a stator comprising features to hold the drive motor without the use of separate fasteners;
e) an impeller, stator, and shroud constructed from injection-molded plastic; and
f) a size and design suited to the cooling of electronic components, most preferably those positioned in the engine compartment of a vehicle.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.